The shy farmer who has traveled far from the southeast by bus to be here gazes at row upon row of human skulls arrayed neatly on wooden shelves, and bursts into tears. Burying her face in her checkered shawl, Ms. Van tries in vain to muffle her sobs. Perhaps, she says, some of the disembodied heads once belonged to her three brothers.

Also visiting the memorial is Nguon Bei, from a farming village in the south. He, too, professes to be taken aback by the gruesome sight – for an entirely different reason. He just can't believe, he says, his old comrades could have done this.

A small man with an unruly mop of hair, Mr. Bei wears a faded UNICEF shirt with a heart emblazoned on it. Until recently, he was a Khmer Rouge stalwart. "I came here to see those thousands of skulls and hundreds of mass graves people are talking about," he adds, glancing furtively around.

Choeung Ek is one of Cambodia's handful of memorials of the Khmer Rouge genocide that, between 1975 and 1979, claimed the lives of nearly 2 million citizens – a third of the nation's population then.

Van and Bei – and 396 fellow villagers from across the country – are here on a two-day, all-expense-paid educational trip organized by the Documentation Center of Cambodia (DC-Cam), a leading research institution on the killing fields.

Mention Cambodia, and the first image that most Westerners think of is heaps of skulls. So it may sound peculiar that numerous survivors – and some perpetrators – themselves have yet to learn about the true extent of the killing fields. During the Khmer Rouge era, rural Cambodians were isolated and resigned to fates imposed by tyrannical overlords. Many still don't understand why they and their families were condemned to extreme suffering, let alone murder, by the Khmer Rouge who proclaimed themselves the liberators of the dispossessed. And governments since have done little to educate them about the period.

"Most survivors living in rural communities have only isolated memories of atrocities," explains Ly Sok Kheang, a researcher for DC-Cam, who is escorting the villagers around memorial sites. "Many don't even know what happened in neighboring provinces."

Every month since February, the research institution, founded by Yale University in 1995, has brought villagers to Phnom Penh in groups of 400 to 500 to show them documentaries, encourage them to share memories, and brief them about war-crimes tribunals slated at long last to start next year in a UN-sponsored trial.

"If [the villagers] can witness the enormity of the crimes," Mr. Kheang adds, "they come to finally understand what happened not only to them personally but to our entire nation."

***

This is what happened to Cambodia: In 1975, under the mantle of "liberation," Pol Pot's peasant army of Maoist guerrillas swept into Phnom Penh and immediately imposed their puritanical vision of a classless, agrarian society. Urbanites, labeled "new people," were herded out into rice paddies to sweat in extreme privation alongside rural "base people." Intellectuals – teachers, doctors, dance instructors, or anyone wearing glasses – were systematically eliminated.

In 1979, invading Vietnamese troops sent the Khmer Rouge fleeing to remote jungles, yet even now several reconstituted ex-Khmer Rouge cadres, including Prime Minister Hun Sen, retain a grip on politics and business.

But this is how Van saw it: With her family broken up and interned in separate communes for men, women, and children, she was forced to toil from 5 a.m. to 10 p.m. while subsisting on a starvation diet and sleeping exposed to the elements under flimsy thatched awnings. A mushroom picked unbidden in the forest could have gotten her killed – everything belonged to Angkar ("the Organization").

One day in 1976, Van recalls planting rice shoots when "[I] saw my brothers being handcuffed [and] I ran over to them." She pats her chest gently to fight back renewed sobs that threaten to contort her open, honest face. "My oldest brother tried to comfort me. He said, 'Little sister, we have to go.' " She was later told her brothers – a rickshaw driver, a fisherman, and a student – had been labeled "enemies of the Revolution" and taken to Toul Sleng, a high-school-turned-prison in Phnom Penh, where inmates were tortured into confessing to trumped-up charges of espionage and sabotage before being killed.

"I still can't believe I survived," she says. In a family of seven siblings, only she and a sister did.

To let Bei tell you, he and many of his brothers-in-arms had nothing to do with the murder of innocents. "I joined the Revolution [in 1976 at age 18] for the good of the country," he says. "I was just a common footsoldier and was politically indoctrinated."

He stripped off his black Khmer Rouge uniform in 1998 when Pol Pot died, and insists he has a clear conscience: "I only killed the enemy." The "enemy" was the "Vietnamese aggressors." But how about all those skulls of his fellow Cambodians displayed at Choeung Ek? Kneading his knuckles, Bei cringes: "I didn't know my comrades were killing Khmers behind our backs."

DC-Cam invites some ex-Khmer Rouge soldiers like Bei on its educational tours to foster reconciliation in villages where victims and their former tormentors often live side by side, the former ostracizing the latter in silent but persistent acts of cold-shouldering.

During an earlier group tour, a woman and her onetime torturer – both from the same province – were seated across from each other in a Phnom Penh hotel dining hall. She fixed him with an accusatory glare but said not a word. He bowed his head in shame and whispered apologies.

"Justice," says DC-Cam's director, Chhang Youk, a survivor of the killing fields himself and Cambodia's foremost researcher on the period, "comes in different forms for different people."

Closure, too, comes in myriad forms. For three decades, Mot Voeun, a diminutive woman, has been waiting for her husband, an erstwhile royalist soldier arrested by the Khmer Rouge.

This morning she saw him again – in a photo displayed in a tableau of former inmates' mug shots at Toul Sleng (now a museum). Just seven of 17,000 men, women, and children brought there survived. What she had always feared but never dared admit to herself was true: He was dead.

Tormented by a tragedy that shattered lives and left questions unanswered, survivors often still can't come to terms with their loss. "My own mother doesn't want to believe her favorite brother is dead," says Mr. Youk. "I found a forced confession by one of his friends that implicated my uncle, but a fortuneteller has told my mother [that] her brother is alive, so she hopes and hopes, waiting for him to return." That's why, he says, education, not just trying a few mass murderers in court, remains crucial. Impoverished Cambodia has a literacy rate of just 35 percent, but there isn't much to read about the Khmer Rouge period, to begin with.

"The Khmer Rouge are not history; they're a living reality," Youk says. "They're still right here among us."

Two-thirds of Cambodia's 12 million citizens were born after the Pol Pot era, so most young Cambodians know little or nothing about the horrors their parents and grandparents experienced. In a 79-page textbook on Cambodian history published for ninth-graders by the Ministry of Education in 2000, the Khmer Rouge era rates two sentences. It has been excised from a later edition.

DC-Cam publishes "Searching for the Truth," a free monthly that contains testimonials by victims and perpetrators alike, and Youk has drafted a comprehensive textbook about the Khmer Rouge for high school students that awaits government approval and funding.

"We're serving the cause of justice just by teaching history – by remembering and commemorating victims," he says.

Van agrees: "So many people died.... If we let our memories of them fade away, their souls will never be at rest and find their peace."